Trainable transceivers for use with electrically operated garage door mechanisms are an increasingly popular home convenience. Such transceivers are typically permanently located in a vehicle and are powered by a vehicle's battery. These trainable transceivers are capable of learning the radio frequency, modulation scheme, and data code of an existing portable remote RF transmitter associated with an existing receiving unit located in the vehicle owner's garage. Thus, when a vehicle owner purchases a new car having such a trainable transceiver, the vehicle owner may train the transceiver to the vehicle owner's existing clip-on remote RF transmitter without requiring any new installation in the vehicle or home. Subsequently, the old clip-on transmitter can be discarded or stored.
If a different home is purchased or an existing garage door opener is replaced, the trainable transceiver may be retrained to match the frequency and code of any new garage door opener receiver that is built into the garage door opening system or one which is subsequently installed. The trainable transceiver can be trained to any remote RF transmitter of the type utilized to actuate garage door opening mechanisms or other remotely controlled devices such as house lights, access gates, and the like. It does so by learning not only the code and code format (i.e., modulation scheme), but also the particular RF carrier frequency of the signal transmitted by any such remote transmitter. After being trained, the trainable transceiver actuates the garage door opening mechanism without the need for the existing separate remote transmitter. Such a trainable transceiver is disclosed in U.S. Pat. No. 5,442,340 which is hereby incorporated by reference.
Trainable transceivers may have several problems including: an antenna that is not tuned at all frequencies, where the transmission range will vary as a function of frequency; and transmission power fluctuations created by various environmental conditions and circuit component manufacturing inconsistencies. Trainable transceivers are limited by the amount of space they may occupy in a vehicle cabin, leading to small antenna types and sizes, such as a loop antenna used in the present invention. In order to effectively use a small loop antenna it must be very high Q and tuned exactly to the operating frequency. High Q can be understood as high efficiency and very narrow bandwidth. The higher the Q, the higher the output field strength will be. However due to the narrow bandwidth limitations of the present invention, slight mistuning can result in significant power reduction.
Trainable transceivers may also vary their power output, as a function of their duty cycle or on-time and with respect to other various environmental variables. It is possible to increase transmission output power and thus transmitter range under certain FCC regulations. The FCC regulations limit the transmission power of a such a transceiver with respect to their duty cycle. The higher the duty cycle, the less power that may be transmitted, as the transmission power level the FCC regulates is averaged over time. Thus, for a transmitter having a low duty cycle the transmission strength may be greater than that of a transmitter having a higher duty cycle.
A further problem present in prior transmitters is the variability of transmission range due to component manufacturing inconsistencies and environmental variables. The transmission range of a transceiver may be affected by temperature. For example, in cold temperatures the power output of a transmitter will be less than that at a warmer temperature. A transmitter should ensure consistent transmission range under all environmental conditions.